Since 2004, graphene has been hailed as one of the most promising materials with the potential to revolutionize applications in electronic devices, such as transistors (suggesting much higher clock speed, e.g., 10-100 GHz) and interconnects, radiofrequency-electronics, energy storage, drug delivery, solar cells, and photonics.
Graphene can be prepared in several ways. Initially, graphene was prepared by exfoliating it from graphite using a scotch tape. This technique has several drawbacks, and it is extremely time consuming. A second method is thermally decomposing graphene directly on a high cost SiC substrates, which requires a very high temperature (>1300° C.) annealing step and high vacuum. The resulting graphene exhibits a small domain structure and oftentimes is non-uniform. Another method entails reducing graphene oxide (GO). GO can be produced from graphitic materials in large quantities at near room temperature. Reduced GO derived graphene has substantial structural defects that affect its mechanical and electrical properties.
Chemical vapor deposition (CVD) has been used to produce high quality graphene by decomposing hydrocarbons, most commonly on catalyst substrates such as metals and metal alloys. The quality and properties of CVD produced graphene depend on the type of the metal catalyst, precursors, hydrocarbon used, reaction temperature and pressure. This method usually requires transferring graphene to an insulating substrate, which is challenging and can compromise graphene properties. Therefore, directly synthesizing graphene on an insulating surface is a topic of interest.
Initially, CVD methods required high deposition temperatures >1000° C. However, in order to achieve mass production of graphene and IC compatible processes, lower temperatures and simpler approaches had to be developed utilizing metal and alloy catalysis and/or alternative carbon sources. Some of these methods still require a high temperature step (˜1000° C.) while others require transferring graphene to an insulating substrate after growth. Tackling both the temperature and transferring issues, low temperature processes that can grow graphene directly on a dielectric layer have been developed. For example, graphene growth at 325° C. using acetylene directly on an insulating substrate and synthesis at 450° C. using a plasma-enhanced chemical vapor deposition process on glass with a Ni catalytic film have been used.